Surface water and ground-water interaction is very active and mutually communicated with each other, while physical and chemical changes in either one influence to the other one. Thus, surface water and groundwater have been recognized as one interplaying resource. Surface water and groundwater interaction is the subject essentially required to research and verify in many aspects such as analysis of hydrological balance, finding of transfer paths of nutrients and contaminants, research and development of groundwater movement systems, securing and planning of water resources, and so on. Surface water and groundwater interaction includes the discharge of water from aquifer (water bearing layer) to surface water layer or recharge of water from surface water layer to water bearing layer. It is desperately required to develop the methods and the means of directly or indirectly measuring the water exchange amount at the surface water/sediment interface in order to quantitatively analyze the discharge and the recharge of water at the surface water/sediment interface.
Until now, various methods have been proposed and employed in order to directly or indirectly measure the mutual interaction and water exchange amount of surface water and groundwater, for example, the method based on modeling, natural tracer, seepage meter, and temperature profiling, or the method of calculating the water exchange by measuring a vertical hydraulic gradient and a vertical hydraulic conductivity (Burnett et al., 2006). Among them, the seepage meter which is normally applied for water exchange measuring means in the search field except for natural tracer, and Darcian flux calculation of measuring water exchange amount by using a vertical hydraulic gradient and a vertical hydraulic conductivity (Mulligan and Charette, 2006) are mostly used. The seepage meter was used in 1940s and 1950s in order to measure water loss amount in irrigation ditches (Israelson and Reeve, 1944), and Lee (1977) designed a half-barrel seepage meter and used for the interaction research and evaluation of groundwater and stream water. As the efforts to solve and overcome the problems and disadvantages raised in the seepage meter by Lee (1977), there have been proposed seepage meters enabled to continuously and automatically measure the water exchange by using various methods, such as Heat pulse (Taniguchi and Fukuo, 1993), Continuous heat pulse (Taniguchi and Iwakawa, 2001), Ultrasonic (Paulsen et al., 2001), Dye-dilution (Sholkovitz et al., 2003), and so on. However, the automatic seepage meters as above are not commercialized yet, and thus, many researchers still use the seepage meter by the method of Lee (1977) for now, but the problem due to low reliability in the measured values by the Lee type seepage meter is still remained (Belanger and Montgomery, 1992).
The Darcian flux calculation as above is the method of calculating Darcian flux (q) from a vertical hydraulic conductivity of the sediment at the surface water interface and a vertical hydraulic gradient. The correctness and preciseness of the measurement results by the Darcian flux depends on the reliability of the values of the vertical hydraulic conductivity and the vertical hydraulic gradient. However, errors occurred when the measurement locations of the vertical hydraulic conductivity and the vertical hydraulic gradient are varied are still raised as problems to be solved.
Therefore, research and development of the means for measuring water exchange at the surface water/sediment interface by the Darcian flux calculation method in order to solve the above problems has been desperately required.